The invention relates generally to methods of directionally drilling wells, particularly wells for the production of hydrocarbon products. More specifically, it relates to a method of automatic control of a steerable drilling tool to drill wells along a planned trajectory.
When drilling oil and gas wells for the exploration and production of hydrocarbons it is often desirable or necessary to deviate a well in a particular direction. Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction.
Directional drilling can be used for increasing the drainage of a particular well, for example, by forming deviated branch bores from a primary borehole. Directional drilling is also useful in the marine environment where a single offshore production platform can reach several hydrocarbon reservoirs by utilizing a plurality of deviated wells that can extend in any direction from the drilling platform.
Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer section of the wellbore to traverse the payzone of a reservoir, thereby permitting increases in the production rate from the well.
A directional drilling system can also be used in vertical drilling operation. Often the drill bit will veer off of a planned drilling trajectory because of an unpredicted nature of the formations being penetrated or the varying forces that the drill bit experiences. When such a deviation occurs and is detected, a directional drilling system can be used to put the drill bit back on course with the well plan.
Known methods of directional drilling include the use of a rotary steerable system (“RSS”). In a RSS, the drill string is rotated from the surface, and downhole devices cause the drill bit to drill in the desired direction. RSS is preferable to utilizing a drilling motor system where the drill pipe is held rotationally stationary while mud is pumped through the motor to turn a drill bit located at the end of the mud motor. Rotating the entire drill string greatly reduces the occurrences of the drill string getting hung up or stuck during drilling from differential wall sticking and permits continuous flow of mud and cuttings to be moved in the annulus and constantly agitated by the movement of the drill string thereby preventing accumulations of cuttings in the well bore. Rotary steerable drilling systems for drilling deviated boreholes into the earth are generally classified as either “point-the-bit” systems or “push-the-bit” systems.
When drilling such a well, an operator typically referred to as a directional driller is responsible for controlling and steering the drill string, or more specifically, the bottom-hole assembly (BHA), to follow a specific well plan. Steering is achieved by adjusting certain drilling parameters, for example, the rotary speed of the drill string, the flow of drilling fluid (i.e., mud), and/or the weight on bit (WOB). The directional driller also typically operates the drilling tools at the end of the drill string so that the drilling direction is straight or follows a curve. These decisions to adjust the tool settings (e.g., the drilling parameters and/or the settings of the drilling tools) are made based on a data set that is measured at the surface and/or measured downhole and transmitted back by the drilling tools. An example of the data transmitted by the tools is the inclination and the azimuth of the well, as both are measured by appropriate sensors, referred to as D&I sensors in oilfield lexicon, in the bottom-hole assembly (BHA).
Typically, these measurements have been taken by static surveys made during the period of time the rotary table is quiescent as a new stand of pipe (approximately ninety feet in length) is attached at the rotary table to permit further drilling. These static survey points form the basis for determining where the BHA is located in relation to the drilling plan given to the directional driller by the geophysicist employed by the owner of the well.
The directional driller is a key link in the success of the drilling operation. The directional driller uses personal experience and judgment to make the decisions required to control the trajectory of the well and thus a level of proficiency and experience is needed to operate the directional drilling controls on the rig during drilling. As this decision making process is neither systematic nor predictable due to the lack of uniformity between wells, formations and BHAs used, directional drillers often differ in their decision making, yet these decisions generally all relate to maintaining the drilling assembly in accordance with a previously detailed well drilling plan. Each drilling program is unique and methods for the systematization of this process are currently being studied by the entire drilling industry. Directional drillers remain in high demand. Thus, there exists a need to automate the control of the directional drilling program to eliminate the need for the real-time supervision of the drilling by the directional driller on each directionally drilled well and to permit the directional driller to assume a more consultative position in the directional drilling process.
Irrespective of whether a directional driller is present on the drilling rig during operations, there exists a need for an improved automatic trajectory control method. Such a method, which can be either automatic or manual, can make the steering of the wells a more systematic, consistent, and predictable task than is provided for by currently existing techniques, while minimizing the reliance on scarce directional drillers to complete drilling programs.